The principal aim of this proposal is to investigate the formation, specificity and role of intercellular junctions during cardiac morphogenesis. The experimental system is based on the reaggregation of dissociated embryonic myocardial cells in rotary suspension culture. Using electron microscopic and biochemical approaches, the development of intercellular contacts will be correlated with changing patterns of nucleic acid and protein biosynthesis. Experimental conditions known to influence cell aggregation, will be examined for their influence on these metabolic patterns. And, in reverse, agents known to modify DNA, RNA and protein synthesis, will be studied for effects on junctional formation. The age and species dependent aggregation of cardiac cells will be examined under conditions in which the kinetics of cell association can be correlated with the formation of structured intercellular junctions. Specificity of these intercellular contacts will be explored in mixed aggregates containing heart cells of different species (mouse vs. chick) or cells of different tissues (heart vs. liver, etc.). Synthesis of cell surface materials, in particular, plasma membrane associated glycoproteins, will be followed during cell aggregation using biochemical, autoradiographic and histochemical procedures. The sum total of this work is aimed at obtaining an integrated picture of surface changes of myocardial cells during the organization of these cells into a functional tissue.